Barrel Length Vs Range and Accuracy

[Crazy_Crystal]

2 hours ago, Adolf Hamster said:

 

it's a very misunderstood topic, hell a lot of folk don't even know it's a thing.

 

funny i'm contemplating doing the math now, years ago for a project i measured the spring energy of an aeg and interestingly for a 1j muzzle energy the spring has ~2.5j of mechanical energy.

 

i suspect a lot of that is lost in the gas heating up under compression (as well as the usual leaks/forcing past the hop etc).

 

problem is it's been years since i've done thermodynamics in any great detail so imma have to polish up on it first lol.

 

from the top of my head the maths shouldn't be too bad. with the primary loss being down to the contraction through the hop/nozzle/cylinder end assembly which would be transferred to thermal energy as you say...

 

oh plus the leak of air around the BB as it travels down the barrel since it's not a perfect seal.... and drag on the BB due to the friction of it touching the hop/barrel as well as the Magnus effect...

 

actually thinking about it, there are a good few factors there... it could be quite an interesting little project if you're that way inclined (sorry I'm a fluids guy 😅)

[Adolf Hamster]

1 minute ago, Crazy_Crystal said:

 

from the top of my head the maths shouldn't be too bad. with the primary loss being down to the contraction through the hop/nozzle/cylinder end assembly which would be transferred to thermal energy as you say...

 

oh plus the leak of air around the BB as it travels down the barrel since it's not a perfect seal.... and drag on the BB due to the friction of it touching the hop/barrel as well as the Magnus effect...

 

actually thinking about it, there are a good few factors there... it could be quite an interesting little project if you're that way inclined (sorry I'm a fluids guy 😅)

 

i'm primarily assuming reversible adiabatic processes for both the compression by the piston and the decompression as the bb starts moving.

 

the problem is you've got to account for the inertia of both the piston and the bb.

 

i'm currently covering all the losses (heat loss, friction, air leak etc) as a single factor of energy lost from the bb at a given stage. of course this doesnt account for the initial pressure peak you'd see as the bb needs a minimum force to even start moving.

 

it's possible to test the frictional losses from pushing through the hop, but if i had access to the equipment i'd also be able to do my actual job....

[Crazy_Crystal]

that seems like a reasonable assumption to me... and at that point you could look at it really simply using the first law where actually all of your loss will be accounted for by Q and work from there.

 

however I think actually the challenge does come down to that pressure loss... although technically that would be considered a second aspect of work done and could be shown as an additional factor of system efficiency. I'll have to think about this some more on my way home from work 🤔

[Adolf Hamster]

2 minutes ago, Crazy_Crystal said:

that seems like a reasonable assumption to me... and at that point you could look at it really simply using the first law where actually all of your loss will be accounted for by Q and work from there.

 

however I think actually the challenge does come down to that pressure loss... although technically that would be considered a second aspect of work done and could be shown as an additional factor of system efficiency. I'll have to think about this some more on my way home from work 🤔

 

suppose that is a fair point, you'd be losing gas volume as well as energy.

 

the main thing i was after finding out was temperature rise, in an hpa for example because the gas is already pressurised and cooled to ambient temperature it's not going to rise in the same way a gas that's just been compressed will.

 

on the flipside a propane gun gets colder as it's sucking all the heat it can to boil any droplets of liquid that make it out of the magazine.

[Crazy_Crystal]

2 hours ago, Adolf Hamster said:

the main thing i was after finding out was temperature rise, in an hpa for example because the gas is already pressurised and cooled to ambient temperature it's not going to rise in the same way a gas that's just been compressed will.

 

on the flipside a propane gun gets colder as it's sucking all the heat it can to boil any droplets of liquid that make it out of the magazine.

 

temperature rise is suddenly a bit more interesting.

 

so as you said the temperature drop for the propane is down to the phase change... for anyone else following, the more shots you fire, the more gas is released and the change from liquid to gas has to get energy to do this from somewhere... cue another discussion on entropy. but at this point I tend to just look at my steam tables in honesty although I will have to check if propane is actually listed... 🤔

 

otherwise thermodynamically I think both the HPA and the GBB system work in a very similar way. they both are a discharge of pressurised fluid out of what is effectively an infinite reservoir, through a valve and down the barrel which actually makes the losses involved in firing the BB quite low in the scheme of things I can only really think of the friction of the valve tbh. at this point it's a game of pressure differentials as far as I can see.

 

However that seems to be quite a different scenario to the losses found in an AEG so I don't know how easily it would be to quantify with a comparison. 🤔

[Adolf Hamster]

2 minutes ago, Crazy_Crystal said:

 

temperature rise is suddenly a bit more interesting.

 

so as you said the temperature drop for the propane is down to the phase change... for anyone else following, the more shots you fire, the more gas is released and the change from liquid to gas has to get energy to do this from somewhere... cue another discussion on entropy. but at this point I tend to just look at my steam tables in honesty although I will have to check if propane is actually listed... 🤔

 

otherwise thermodynamically I think both the HPA and the GBB system work in a very similar way. they both are a discharge of pressurised fluid out of what is effectively an infinite reservoir, through a valve and down the barrel which actually makes the losses involved in firing the BB quite low in the scheme of things I can only really think of the friction of the valve tbh. at this point it's a game of pressure differentials as far as I can see.

 

However that seems to be quite a different scenario to the losses found in an AEG so I don't know how easily it would be to quantify with a comparison. 🤔

 

hence my curiosity to do the math.

 

in one system you're starting out at ambient, the other you're starting out pre-pressurised, and of course the volume is practically limitless (at least assuming the dwell on the poppet has been properly set for the ammo weight)